Magnetic disk device and reordering method

ABSTRACT

According to one embodiment, a magnetic disk device includes a first head which writes and reads to the first disk, a second head which writes data and reads data to the second disk, a first actuator including the first head, a second actuator including the second head, and a controller which performs a first reordering process for a command scored in a first queue corresponding to the first actuator and performs a second reordering process for a command stored in a second queue corresponding to the second actuator, wherein the controller selects a first command to be executed next by the first actuator based on current and future operating states of the second actuator, and executes the first command.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2021-038243, filed Mar. 10, 2021, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic disk deviceand a reordering method.

BACKGROUND

A magnetic disk device performs a reordering process of storing aplurality of commands transferred from a host or the like in a queue andrearranging the order in which the commands stored in the queue areprocessed. A split actuator magnetic disk device including a pluralityof actuators has recently been proposed. In the split actuator magneticdisk device, the actuators are controlled independently. The splitactuator magnetic disk device stores a plurality of commandscorresponding to each of the actuators in a queue corresponding to eachof the actuators, and reorders the commands stored in the queuecorresponding to each of the actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a configuration of amagnetic disk device according to an embodiment.

FIG. 2 is a plan view showing an example of the placement of a headrelative to a disk.

FIG. 3 is a schematic diagram snowing an example of a queue.

FIG. 4 is a time sequence showing an example of a reordering processaccording to the embodiment.

FIG. 5 is a schematic diagram snowing an example of read/write operationaccording to the embodiment.

FIG. 6 is a schematic diagram showing an example of a change in a seekcurrent corresponding to the head of an actuator according to theembodiment and a change in a position error signal of the head ofanother actuator.

FIG. 7 is a schematic diagram showing an example of the change in a seekcurrent corresponding to the head of an actuator according to theembodiment and the change in a position error signal of the head ofanother actuator.

FIG. 8 is a schematic diagram showing an example of the change in a seekcurrent corresponding to the head of an actuator according to theembodiment and the change in a position error signal of the head ofanother actuator.

FIG. 9 is a schematic diagram showing an example of a reordering tableaccording to the embodiment.

FIG. 10 is a flowchart showing an example of the reordering processaccording to the embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk devicecomprises: a first disk; a second disk; a first head which writes datato the first disk and reads data from the first disk; a second headwhich writes data to the second disk and reads data from the seconddisk; a first actuator including the first head; a second actuatorincluding the second head; and a controller which performs a firstreordering process for a command stored in a first queue correspondingto the first actuator and performs a second reordering process for acommand stored in a second queue corresponding to the second actuator,wherein the controller selects a first command to be executed next bythe first actuator based on current and future operating states of thesecond actuator, and executes the first command.

An embodiment will be described below with reference to the drawings.The drawings are only one example and do not limit the scope of theinvention.

Embodiment

FIG. 1 is a schematic diagram showing an example of a configuration of amagnetic disk device 1 according to an embodiment.

The magnetic disk device 1 includes a housing HS, a head disk assembly(HDA) 10, a driver IC 20, a head amplifier integrated circuit (referredto as a head amplifier IC or a preamplifier hereinafter) 30, a volatilememory 70, a buffer memory (buffer) 80, a nonvolatile memory 90, and asystem controller 130 that is a one-chip integrated circuit. Themagnetic disk device 1 is connected to a host system (referred to simplyas a host hereinafter) 100. The magnetic disk device 1 is a splitactuator magnetic disk device capable of independently driving aplurality of actuators AC to be described later. The magnetic diskdevice 1 includes a plurality of actuators AC, for example, twoactuators (actuators AC0 and AC1 to be described later). Note that themagnetic disk device 1 may include three or more actuators AC. Themagnetic disk device 1 is capable of driving the actuators AC inparallel and reading and writing data in parallel by the head on each ofthe actuators.

The housing HS has a bottom wall HSB. FIG. 1 shows as if the housing HShad only the bottom wall HSB, but, in practice, the housing HS has notonly the bottom wall HSB but also sidewalls standing along the peripheryof the bottom wall HSB, and a cover that blocks an opening in a baseformed by the bottom wall HSB and the sidewalls.

The HDA 10 includes a magnetic disk (referred to as a disk hereinafter)DK, a head HD, a spindle motor (referred to as an SPM hereinafter) 13that rotates a spindle 12, an arm AM, an actuator block BK, a voice coilmotor (referred to as a VCM hereinafter) 14, a suspension 15, and amicro-actuator (referred to as an MA hereinafter) 16. Note that the HDA10 need not include the MA 16. If the HDA 10 does not include the MA 16,the head HD may be mounted on the arm AM. FIG. 1 shows a section of theHDA 10.

The SPM 13 is attached to the bottom wall HSB. The spindle 12 isattached to a central part of the SPM 13.

The disk DK includes a plurality of disks DK. The disk DK is attached tothe spindle 12 and rotated by driving the SPM 13. The disk DR has afront surface (or a top surface) and a back surface (or a bottomsurface) opposed to the front surface (or the top surface). Hereinafter,the front surface (or the top surface; and/or the back surface or thebottom surface) may also be simply referred to as a disk. In the exampleshown in FIG. 1, the disk DK includes disks DK0 and DK1. The disks DK0and DK1 are attached to the spindle 12. The disk DK0 is placed above thedisk DK1, for example. In other words, the disk DK1 is placed, forexample, between the disk DK0 and the bottom wall HSB. The disk DK0 hasa top surface S00 and a bottom surface S01 opposed to the top surfaceS00. The disk DK1 has a top surface 300 and a bottom surface S01 opposedto the top surface S00. Note that the disk DK may include three or moredisks. Hereinafter, a direction along the circumference of the disk DK(the top and bottom surfaces of the disk DK) will be referred to as acircumferential direction, and a direction orthogonal to thecircumferential direction of the disk DK (the top and bottom surfaces ofthe disk DK) will be referred to as a radial direction. The radialdirection corresponds to a direction toward the inner circumferentialside and the outer circumferential side on the disc DK (the top andbottom surfaces of the disk DK).

The head HD includes a plurality of heads HD. The head HD faces the diskDK. The head HD includes a write head WH for writing data to the disk DKand a read head RH for reading data from the disk DK. Hereinafter, “aprocess of writing data to the disk DK” may be referred to as “a writeprocess” and “a process of reading data from the disk DK” may bereferred to as “a read process”. In addition, “recording data in aparticular recording area”, “reading data from a particular recordingarea”, “placing the head HD in a particular position of the disk DK”,“writing data to a particular area of the disk DK”, “reading data from aparticular area of the disk DK”, “communicatively connecting to aparticular area” and the like may be referred to as “accessing”.

In the example shown in FIG. 1, the head HD includes heads HD0 and HD1.The head HD0 includes, for example, a head HD00 facing the top surfaceS00 of the disk DK0 and a head HD01 facing the bottom surface S01 of thedisk DK0. Note that the head HD0 may include only one head or three ormore heads. The head HD0 includes a write head WH0 for writing data tothe disk DK0 and a read head RH0 for reading data written to the diskDK0. The write head WH0 includes a write head WH00 and a write headWH01. The read head RH0 includes a read head RH00 and a read head RH01.

The head HD00 includes a write head WH00 for writing data to the topsurface S00 of the disk DK0 and a read head RH00 for reading data fromthe top surface S00 of the disk DK0. The head HD01 includes a write headWH01 for writing data to the bottom surface S01 of the disk DK0 and aread head RH01 for reading data from the bottom surface S01 of the diskDK0.

The head HD1 includes, for example, a head HD10 facing the top surfaceS10 of the disk DK1 and a head HD11 facing the bottom surface S11 of thedisk DK1. Note that the head HD1 may include only one head or three ormore heads. The head HD1 includes a write head WH1 for writing data tothe disk DK1 and a read head RH1 for reading data from the disk DK1. Thewrite head WH1 includes a write head WH10 and a write head WH 11. Theread head RH1 includes a read head RH10 and a read head RH11.

The head HD10 includes a write head WH10 for writing data to the topsurface S10 of the disk DK1. and a read head RH10 for reading data fromthe top surface S10 of the disk DK1. The head HD1 includes a write headWH11 for writing data to the bottom surface S11 of the disk DK1 and aread head RH11 for reading data from the bottom surface S11 of the diskDK1.

The actuator block BK includes a plurality of actuator blocks BK. Theactuator block BK is rotatably attached to a bearing BR standing on thebottom wall HSB. In the example shown in FIG. 1, the actuator block BKincludes actuator blocks BK0 and BK1. The actuator blocks BK0 and BK1are rotatably attached to the bearing BR standing on the bottom wallHSB. The actuator block BK0 is placed on the actuator block BK1. Inother words, the actuator block BK1 is located between the bottom wallHSB and the actuator block BK0.

The arm AM includes a plurality of arms AM. The arm AM is connected tothe actuator block BK. In the example shown in FIG. 1, the arm AMincludes arms AM0 and AM1. The arm AM0 is placed above the arm AM1. Inother words, the arm AM1 is placed between the arm AM0 and the bottomwall HSB of the housing HS. The arm AM may include only one arm or threeor more arms depending on the number of actuators AC.

The arm AM0 includes, for example, an arm AM00 located alongside the topsurface S00 of the disk DK0 and an arm AM01 located alongside the bottomsurface S01 of the disk DK0. Note that the arm AM0 may include only onearm or three or more arms depending on the number of heads HD0. The armAM0 is connected to the actuator block BK0.

The arm AM1 includes, for example, an arm AM10 located alongside the topsurface S10 of the disk DK1 and an arm AM11 located alongside the bottomsurface S11 of the disk DK1. Note that the arm AM1 may include only onearm or three or more arms depending on the number of heads 101. The armAM1 is connected to the actuator block BK1.

The VCM 14 includes a plurality of VCMs 14. The VCM 14 is connected tothe actuator block BK on the opposite side of the arm AM. In the exampleshown in FIG. 1, the VCM 14 includes VCMs 140 and 141. The VCM 140 isconnected to the actuator block BK0 on the opposite side of the arm AM0.The VCM 141 is connected to the actuator block BK1 on the opposite sideof the arm AM1. The VCM 14 may include only one VCM or may have three ormore VCMs depending on the number of actuator blocks BK.

The suspension 15 includes a plurality of suspensions 15. The suspension15 is attached to the arm AM. The distal end portion of the suspension15, which is opposed to the other end portion of the suspension 15connected to the arm AN, is provided with the head HD. In the exampleshown in FIG. 1, the suspension 15 includes a suspension 150 and asuspension 151. The suspension 150 is placed above the suspension 151.In other words, the suspension 151 is placed between the suspension 150and the bottom wall HSB of the housing HS. The suspension 15 may includeonly one suspension or three or more suspensions depending on the numberof arms AM.

The suspension 150 is attached to the arm AM0. The distal end portion ofthe suspension 150, which is opposed to the other end portion of thesuspension 150 connected to the arm AM0, is provided with the head HD0.The suspension 150 includes, for example, a suspension 1500 attached tothe arm AM00 and a suspension 1501 attached to the arm AM01. The distalend portion of the suspension 1500, which is opposed to the other endportion of the suspension 1500 connected to the arm AM00, is providedwith the head HD00. The distal end portion of the suspension 1501, whichis opposed to the other end portion of the suspension 1501 connected tothe arm AM01, is provided with the head HD01. Note that the suspension150 may include only one suspension or may have three or moresuspensions depending on the number of arms AM0.

The suspension 151 is attached to the arm AM1. The distal end portion ofthe suspension 151, which is opposed to the other end portion of thesuspension 151 connected to the arm AM1, is provided with the head HD1.The suspension 151 includes, for example, a suspension 1510 attached tothe arm AM10 and a suspension 1511 attached to the arm AM11. The distalend portion of the suspension 1510, which is opposed to the other endportion of the suspension 1510 connected to the arm AM10, is providedwith the head HD10. The distal end portion of the suspension 1511, whichis opposed to the other end portion of the suspension 1511 connected tothe arm AM11, is provided with the head HD11. The suspension 151 mayinclude only one suspension or may have three or more suspensionsdepending on the number of arms AM1.

The MA 16 includes a plurality of MAs 16. The MA 16 is attached to thearm AM or the suspension 15 or the head HD. The MA 16 finely controlsthe operation of the head HD in the radial direction. For example, theMA 16 controls the operation of the head HD in the radial direction morefinely than the operation of the head HD in the radial direction by theVCM 14.

In the example shown in FIG. 1, the MA 16 includes an MA 160 and an MA161. The MA 160 is attached to the suspension 150. The MA 160 finelycontrols the operation of the head HD0 in the radial direction. Forexample, the MA 160 controls the operation of the head HD0 in the radialdirection more finely than the operation of the head HD0 in the radialdirection by the VCM 140. The MA 160 includes, for example, an MA 1600attached to the suspension 1500 and an MA 1601 attached to thesuspension 1501. The MA 1600 finely controls the operation of the headHD00 in the radial direction. For example, the MA 1600 controls theoperation of the head HD00 in the radial direction more finely than theoperation of the head HD00 in the radial direction by the VCM 140. TheMA 1601 finely controls the operation of the head HD01 in the radialdirection. For example, the MA 1601 controls the operation of the headHD01 in the radial direction more finely than the operation of the headHD01 in the radial direction by the VCM 140. Note that the MA 160 mayinclude only one MA or may have three or more MAs depending on thenumber of suspensions 150.

The MA 161 is attached to the suspension 151. The MA 161 finely controlsthe operation of the head HD1 in the radial direction. For example, theMA 161 controls the operation of the head HD1 in the radial directionmore finely than the operation of the head HD1 in the radial directionby the VCM 141. The MA 161 includes, for example, an MA 1610 attached tothe suspension 1510 and an MA 1611 attached to the suspension 1511. TheMA 1610 finely controls the operation of the head HD10 in the radialdirection. For example, the MA 1610 controls the operation of the headHD0 in the radial direction more finely than the operation of the headHD10 in the radial direction by the VCM 141. The MA 1611 finely controlsthe operation of the head HD11 in the radial direction. For example, theMA 1611 controls the operation of the head HD11 in the radial directionmore finely than the operation of the head HD11 in the radial directionby the VCM 141. Note that the MA 161 may include only one MA or may havethree or more MAs depending on the number of suspensions 151.

The actuator AC includes a plurality of actuators AC. Each of theactuators AC is turnably (or rotatably) attached to the bearing BR. Inother words, the actuators AC turn independently around the bearing BR.Note that the actuators AC may turn in parallel around the bearing BP.Each of the actuators AC includes a suspension 15, an MA 16, an arm AM,an actuator block BK and a VCM 14. Each of the actuators AC drives theVCM 14 around the bearing BR and finely drives the MA 16 to set the headHD mounted on the suspension 15 in a particular position of the disk DK.When each of the actuators AC does not include the MA 16, it drives theVCM 14 around the bearing BR to set the head HD mounted on thesuspension 15 in a particular position of the disk DK.

In the example shown in FIG. 1, the actuator AC includes actuators AC0and AC1. The actuator AC0 is placed on the actuator AC1. In other words,the actuator AC1 is placed between the bottom wall HSB and the actuatorAC0. Note that three or more actuators AC may be provided.

The actuator AC0 is rotatably attached to the bearing BR. The actuatorAC0 includes a suspension 150, an MA 160, an arm AM0, an actuator blockBK0 and a VCM 140. The actuator AC0 drives the VCM 140 around therotational axis of the bearing BR and finely drives the MA 160 to setthe head HD0 mounted on the suspension 150 in a particular position ofthe disk DK0. When the actuator AC0 does not include the MA 160, itdrives the VCM 140 around the bearing BR to set the head HD0 mounted onthe suspension 150 in a particular position of the disk DK0.

The actuator AC1 is rotatably attached to the bearing BR. The actuatorAC1 includes a suspension 151, an MA 161, an arm AM1, an actuator blockBK1 and a VCM 141. The actuator AC1 drives the VCM 141 around therotational axis of the bearing BR and finely drives the MA 161 to setthe head HD1 mounted on the suspension 151 in a particular position ofthe disk DK1. When the actuator ACM does not include the MA 161, itdrives the VCM 141 around the bearing BR to set the head HD1 mounted onthe suspension 151 in a particular position of the disk DK1.

FIG. 2 is a plan view showing an example of the placement of the head HDrelative to the disk DK. As shown in FIG. 2, the direction toward theouter periphery of the disk DK in the radial direction will be referredto as an outward direction (outside), and the direction opposite to theoutward direction will be referred to as an inward direction (inside).The direction in which the disk DK rotates in the circumferentialdirection will be referred to as a rotational direction. The rotationaldirection is a counterclockwise direction in the example shown in FIG.2, but may be an opposite direction (clockwise direction).

In the disk DK, a user data area DKa which is available from a user anda system area DKb to which information necessary for system management(also referred to as system information hereinafter) is written, areallocated to an area to which the data of the disk DK can be written.Hereinafter, a particular position of the disk DK in its radialdirection may be referred to as a radial position, and a particularposition of the disk DK in its circumferential direction may be referredto as a circumferential position. The radial position and thecircumferential position may also be referred to simply as a position.For example, the radial position corresponds to the position of a trackor a sector (data sector) in the radial direction, and thecircumferential position corresponds to the position of a sector in aparticular track in the circumferential direction. For example, theposition corresponds to the position of a sector (data sector) in thedisk DK. The position of a sector (data sector) can be indicated by atleast one of a cylinder (track) number including a particular sector, ahead number of the head HO accessing a particular sector, a sectornumber of a particular sector, a radial position of a particular sectorin the disk DK, and a disk angle of a particular sector. For example,the position of a sector is indicated by the combination of three of thecylinder (track) number including a particular sector, head number ofthe head HD accessing a particular sector, sector number of a particularsector, radial position of a particular sector in the disk DK, and diskangle of a particular sector. The disk DK may include at least onetrack. Hereinafter, the term “track” will be used in various meaningssuch as “one of a plurality of areas into which the disk DK is dividedin the radial direction”, “data written to the circumference of the diskDK”, and “a path along the circumference of the disk DK”. The trackincludes a plurality of sectors. The term “sector” will be used invarious meanings such as “one of a plurality of areas into which a trackis divided in the circumferential direction” and “data written to one ofthe areas into which a track is divided in the circumferentialdirection”. In the example shown, in FIG. 7, a user data area DKa0 and asystem area DKb0 are allocated to the disk DK0. Alternatively, a userdata area DKa1 and a system area DKb1 are allocated to the disk DK1.

The disk DK includes a plurality of servo areas (also be referred to asservo patterns or servo data hereinafter), which are not shown. Theservo patterns, for example, extend radially in the radial direction ofthe disk DK and are arranged discretely at particular intervals in thecircumferential direction. Servo data including preamble, servo mark,gray code, PAD, burst data, post code and the like is written to theservo pattern. User data is written to the user data area DKa other thanthe servo patterns.

The head HD slides in the horizontal plane of the disk DK when theactuator AC rotates around the bearing BR during seeking, for example.In the example shown in FIG. 2, the head HD0 slides in the horizontalplane of the disk DK0 when the actuator AC0 rotates around the bearingBR during seeking, for example. In addition, the head HD1 slides in thehorizontal plane of the disk DK1 when the actuator ACM rotates aroundthe bearing BR during seeking, for example.

The driver IC 20 controls the driving of the SPM 13 and VCM 14 (VCMs 140and 141) under the control of the system controller 130 (specifically,MPU 50 or HDC 60 to be described later. The driver IC 20 is electricallyconnected to the SPM 13 and VCM 14 (VCMs 140 and 141). The driver IC 20is connected to, for example, the SPM 13 through a particular interface.The driver IC 20 is connected to, for example, each of the VCMs 140 and141 through an interface.

The driver IC 20 includes an SPM control unit 210, a first VCM controlunit 220, a second VCM control unit 221, a first microactuator (MA)control unit 230 and a second microactuator (MA) control unit 231. TheSPM control unit 210 controls the rotation of the SPM 13. The first VCMcontrol unit 220 controls the current (or the voltage) supplied to theVCM 140 to control the driving of the VCM 140. The second VCM controlunit 221 controls the current (or the voltage) supplied to the VCM 141to control the driving of the VCM 141. The first MA control unit 230controls the current (or the voltage; supplied to the MA 160 to controlthe drive of the MA 160. The second MA control unit 231 controls thecurrent (or the voltage) supplied to the MA 161 to control the drivingof the MA 16. Note that the system controller 130 may include some ofthe components of the driver IC 20 (e.g., the SPM control unit 210,first VCM control unit 220, second VCM control unit 221, first MAcontrol unit 230 and second MA control unit 231). If the actuator AC0does not include the MA 160 or the actuator AC1 does not include the MA161, the first MA control unit 230 and the second MA control unit 231 isunnecessary. In addition, two or more driver ICs 20 may be provideddepending on the number of actuators AC.

The head amplifier IC (preamplifier) 30 amplifies a read signal readfrom the disk DK and outputs the amplified read signal to the systemcontroller 130 (specifically, a read/write (R/W) channel 40 to bedescribed later). The head amplifier TC 30 supplies the head HD with awrite current corresponding to the write data output from the systemcontroller 130 (specifically, the R/W channel 40 to be described later).The head amplifier IC 30 is electrically connected to each actuator AC,for example, the actuator AC0 and the actuator AC1. The head IC 30 isconnected to each actuator AC through an interface IF. For example, thehead IC 30 is connected to the actuator AC1 through an interface IF0 andconnected to the actuator AC2 through an interface IF. For example, thehead IC 30 transmits/receives a signal to/from the actuator AC1 throughthe interface IF0, and transmits/receives a signal to/from the actuatorAC2 through the interface IF1. The head amplifier IC 30 is electricallyconnected to each head HD, for example, the head HD0 and the head HD1through the interface IF. For example, the head amplifier IC 30 iselectrically connected to the head HD0 through the interface IF0 andelectrically connected to the head HD1 through the interface IF1. Thehead amplifier IC 30 supplies the head HD with a write currentcorresponding to a signal output from the R/W channel 40 via theinterface IF, and receives a read signal from the head HD via theinterface IF. For example, the head amplifier IC 30 supplies the headHD0 with a write current corresponding to a signal output from the R/Wchannel 40 via the interface IF0, and receives a read signal from thehead HD0 via the interface IF0. For example, the head amplifier IC 30supplies the head HD1 with a write current corresponding to a signaloutput from the R/W channel 40 via the interface IF1, and receives aread signal from the head HD1 via the interface IF1.

The head amplifier IC 30 includes a first read head selection unit 320,a second read head selection unit 321, a first read signal detectionunit 330 and a second read signal detection unit 331. The first readhead selection unit 320 selects a read head RH0 that reads data from thedisk DK0 in the actuator AC0. The second read head selection unit 321selects a read head RH1 that reads data from the disk DK1 in theactuator AC1. The first read signal detection unit 330 detects a signal(read signal) read from the disk DK0 by the read head RH0. The secondread signal detection unit 331 detects a signal (read signal) read fromthe disk DK1 by the read head RH1. Note that the system controller 130may include some of the components of the head amplifier IC 30 (e.g.,the first read head selection unit 320, second read head selection unit321, first read signal detection unit 330 and second read signaldetection unit 331). In addition, two or more head amplifier ICs 30 maybe provided depending on the number of actuators AC.

The volatile memory 70 is a semiconductor memory from which stored datais lost when power supply is cut off. The volatile memory 70 stores dataand the like necessary for processing in each component of the magneticdisk device 1. The volatile memory 70 is, for example, a dynamic randomaccess memory (DRAM) or a synchronous dynamic random access memory(SDRAM).

The buffer memory 50 is a semiconductor memory which temporarily recordsdata and the like transmitted and received between the magnetic diskdevice 1 and the host 100. Note that the buffer memory 80 may beintegrated with the volatile memory 70. The buffer memory 80 is, forexample, a DRAM, a static random access memory (SRAM), an SDRAM, aferroelectric random access memory (FeRAM) or a magnetoresistive randomaccess memory (MRAM).

The nonvolatile memory 90 is a semiconductor memory that records storeddata even when power supply is cut off. The nonvolatile memory 90 is,for example, a NOR type or a NAND type flash read only memory (FROM).

The system controller (controller) 130 is implemented using, forexample, a large-scale integrated circuit (LSI) called asystem-on-a-chip (SoC) in which a plurality of elements are integratedon a single chip. The system controller 130 includes the read/write(R/W) channel 40, microprocessor (MPU) 50 and hard disk controller (HDC)60. The system controller 130 is electrically connected to the driver IC20, head amplifier IC 30, volatile memory 70, buffer memory 80,nonvolatile memory 90 and host system 100. Note that the systemcontroller 130 may include the SPM control unit 210, first VCM controlunit 220, second VCM control unit 221, first read head selection unit320, second read head selection unit 321, first read signal detectionunit 330 and second read signal detection unit 331. The systemcontroller 130 may include the driver IC 20 and head amplifier IC 30. Inaddition, two or more system controllers 130 may be provided dependingon the number of actuators AC.

The R/W channel 40 executes signal processing for read data transferredfrom the disk DK to the host 100 and write data transferred from thehost 100 in response to an instruction from the MPU 50 to be describedlater. The R/W channel 40 has a circuit or a function for measuring thesignal quality of read data. The R/W channel 40 is electricallyconnected to, for example, the head amplifier IC 30, MPU 50 and HDC 60.Note that two or more R/W channels 40 may be provided depending on thenumber of actuators AC.

The MPU 50 is a main controller that controls each component of themagnetic disk device 1 in response to an instruction from the host 100or the like. The MPU 50 controls the actuator AC through the driver IC20 to perform servo control for positioning the head HD. For example,the MPU 50 controls the actuators AC0 and AC1 independently or inparallel through the driver IC 20. The MPU 50 controls the operation ofwriting data to the disk DK and selects a storage destination of writedata. The MPU 50 also controls the operation of reading data from thedisk OK and controls processing of read data. The MPU 50 is connected toeach component of the magnetic disk device 1. The write operationincludes an operation from the reception of a command to the completionof write of data to a particular area, such as a seek operation, arotational delay, and a write process. The read operation includes anoperation from the reception of a command to the completion of read ofdata from a particular area, such as, a seek operation, a rotationaldelay, and a write process. The MPU 50 is electrically connected to thedriver IC 20, R/W channel 40, HDC 60, and the like. Note that two ormore MPU's 50 may be provided depending on the number of actuators AC.

In response to an instruction from the MPU 50, the HDC 60 controls theread/write process and controls data transfer between the host 100 andthe R/W channel 40. The HDC 60 is electrically connected to the R/Wchannel 40, MPU 50, volatile memory 70, buffer memory 80, nonvolatilememory 90, and the like. Note that two or more HDCs 60 may be provideddepending on the number of actuators AC.

The HDC 60 includes a servo control unit 610 and a command control unit620. The HDC 60 executes the process of each of the units on firmware.Note that the HDC 60 may include each of the units as a circuit. Inaddition, some of the components of the HDC 60 may be included in theMPU 50. For example, the servo control unit 610 and the command controlunit 620 may be included in the MPU 50.

The servo control unit 610 controls the position of the head HD. Inother words, the servo control unit 610 controls access to a particulararea of the disk DK by the head HD. The servo control unit 610 includesa tracking control unit 6100 and a seek control unit 6101. Note that twoor more servo control units 610 may be provided depending on the numberof actuators AC.

The tracking control unit 6100 controls tracking of the head HD to aparticular track of the disk DK. “Tracking the head HD to a particulartrack of the disk DK” may also be referred to simply as “tracking”. The“tracking” includes “following a particular path or a particular trackwhen data is written to the disk DK” and “following a particular path ora particular track when data is read from the disk DK”.

The seek control unit 6101 controls a seek of the head HD from aparticular track to a target track in the disk DK.

The command control unit 620 controls commands received from the host100 or the like. For example, the command control unit 620 storescommands received from the host 100 or the like in a queue in the orderreceived from the host 100 or the like. Based on a particular one of thecommands stored in the queue, the command control unit 620 gains accessto a position or an area specified by the command, for example, asector, through the servo control unit 610. Hereinafter, “gaining accessto a position or an area specified by a particular command based on thecommand” may also be referred to as “processing a command”. The“commands stored in a queue” may also be referred to as “queuedcommands”. Further, “storing commands in a queue” may also be referredto as “queuing”.

The command control unit 620 detects or estimates the present and futureoperating states of an actuator AC to be currently controlled (which mayalso be referred to as an own actuator hereinafter) and the present andfuture operating states of an actuator AC other than the own actuator(which may also be referred to as the other actuator hereinafter). Theoperating states of the actuator AC includes a command executing state,a read/write process executing state, a seek state of a head HDcorresponding to the actuator AC, a head position corresponding to theactuator AC, a head velocity corresponding to the actuator AC, a headacceleration corresponding to the actuator AC, a state of timing (orscheduled time) at which a write/read process is started by a head HDcorresponding to the actuator AC, a state of timing (or scheduled time)at which a write/read process is terminated by a head HD correspondingto the actuator AC, and the like. Based on the present and futureoperation states of the own actuator AC and the other actuator AC, thecommand control unit 620 selects a particular command from the queuecommands stored in the queue for each interface IF (or the actuator AC)in the order received from the host 100 or the like, and replaces theorder of the selected command with the order (which may also be referredto as the subsequent order hereinafter) of a command to be processednext to the currently-processed command (which may also be referred toas the current command), thereby to process the selected command after(or during) the processing of the current command. Hereinafter,“replacing the order of a plurality of commands to be processed” mayalso be referred to as “command reordering” or simply “reordering”.“Performing a particular arithmetic operation (computation), selecting aparticular command from the commands based on the result of theparticular arithmetic operation (computation), and reordering the orderof the selected command” may also be referred to as “reorderingarithmetic process”, “reordering arithmetic operation” or “reorderingprocess”. In addition, the “command to be processed next to the currentcommand” may also be referred to as “next processed command”.

For example, based on the current and future operating states of the ownactuator AC and the other actuator AC, the command control unit 620 mayperform a reordering process for each interface IF (or the actuator AC)to process commands independently or in parallel for each interface IF(or the actuator AC) and to process commands within a single process foreach interface IF (or the actuator AC). The command control unit 620 maystart to process commands in an event-driven mode or a time-driven mode(time-shared mode), for example.

While the command control unit 620 is processing the current command, itperforms an arithmetic operation based on the position of the disk OKwhere the head HD is currently placed, for example, the position of adata sector of the disk DK where the head HD is currently placed (whichmay also be referred to simply as the current position hereinafter) anda plurality of queue commands stored in the queue for each interface IF(or the actuator AC) in the order received from the host 100 or thelike, and performs a reordering process based on the result of thearithmetic operation, thereby processing the next-processed command.

Based on the current and future operating states of the own actuator ACand the other actuator AC, the current position of a head HDcorresponding to the own actuator AC, a plurality of queue commandsstored in the queue for each interface IF (or the actuator AC) in theorder received from the host 100 or the like, and a table (which mayalso be referred to as a reordering table or a seek profile tablehereinafter) indicating the relationship in the seek distance and seektime of the head HD between the own actuator AC and the other actuatorAC, the command control unit 620 calculates a plurality of times forgaining access to the position (which may also be referred to simply asa position hereinafter) of each of the sectors (data sectors) of thedisk DK designated by the queue commands from the current position.Hereinafter, “a time period for which the head HD gains access to asector (data sector) in a particular position of the disk DK (a timeperiod required to place the head HD)” may also be referred to as“access cost”. The access cost includes a time period for seeking thehead HD from a particular track of the disk DK to a track other than thetrack (which may also be referred to as seek time hereinafter), and arotational delay for placing the head HD at a particular disk angle of aparticular sector other than the sector of the disk DK. The reorderingtable may vary, for example, from head HD to head HD or from actuator ACto actuator AC or the same reordering table may be used for some of theheads HD or for some of the actuators AC or the same reordering tablemay be used for all of the heads HD and for all of the actuators AC. Inorder to reduce the influence of vibration and power consumption of themagnetic disk device 1, the command control unit 620 may adjust theaccess cost by weighting the calculated access cost (e.g., multiplyingor dividing a given value) and radially offsetting the position of thedisk DK where the head HD starts to move and the position of the disk DKwhere the head HD moves (e.g., adding or subtracting a given value) tocalculate the access cost.

Based on the current and future operating states of the own actuator AC(e.g., the current position of a head HD corresponding to the ownactuator AC), the current and future operating states of the otheractuator AC, and the result of calculation of access costs correspondingto the queue commands of the own actuator AC and other actuator ACstored in the queue for each interface IF (or the actuator AC), thecommand control unit 620 selects, as a next-processed command, a command(which may also be referred to as a low-cost command hereinafter) forspecifying a position accessible at an access cost, which is shorter (orsmaller) than the cost of access to a position specified by a commanddifferent from the current command (which may also be referred to as adifferent command hereinafter) from the current position of a head HDcorresponding to the own actuator AC, from at least one of the queuecommands of the own actuator AC and the other actuator AC, and thenchanges the order of the low-cost command selected in at least one ofthe queue commands to the next order. Hereinafter, information for thereordering arithmetic process, such as information on the current andfuture operating states of the own actuator AC and other actuator AC,information on a plurality of queue commands corresponding to the ownactuator AC and other actuator AC, information on a plurality ofpositions respectively designated by the queue commands corresponding tothe own actuator AC and other actuator AC, reordering tables of the ownactuator AC and other actuator AC, and information on seeking from thecurrent position of the head HD to a plurality of positions respectivelydesignated by the queue commands corresponding to the own actuator ACand other actuator AC, may also be referred to as reorderinginformation. Note that the reordering information may not include areordering table. The reordering information may include informationother than the above information. The position information correspondsto, for example, at least one information of a head, a track, a sector,a radial position and a disk angle, or information of a combinationthereof. Hereinafter, for convenience of description, “cost of accessfrom a particular position to another position” may also be referred toas “access cost of a particular command” or “access cost correspondingto a particular command”. As described above, the command control unit620 calculates access cost corresponding to each queue command of theown actuator AC and the other actuator AC based on the reorderinginformation, selects a low-cost command from the queue commands based onthe result of calculation of the access cost, performs a reorderingarithmetic process for changing the order of the selected low-costcommand to the next order, and processes the low-cost command afterprocessing the current command. The command control unit 620 may recordthe reordering information in a particular recording area, such as thesystem area DKb of the disk DK, the volatile memory 70, the buffermemory 80, and the nonvolatile memory 90. Note that the command controlunit 620 may record the reordering information other than the reorderingtable in a particular recording area, such as the system area DKb of thedisk DK, the volatile memory 70, the buffer memory 80, and thenonvolatile memory 90. In this case, the command control unit 620 mayrecord the reordering table in a particular recording area, such as thesystem area DKb of the disk DK, the volatile memory 70, the buffermemory 80, and the nonvolatile memory 90, separately from the reorderinginformation. The command control unit 620 may also calculate thereordering table.

For example, based on the reordering information, the command controlunit 620 calculates a plurality of access costs of the queue commands ofthe own actuator AC and other actuator AC stored in the queue for eachinterface IF (or the actuator AC). Based on the reordering informationand the result of the calculation of the access costs, a command controlunit 620 selects a command (which may also be referred to as thelowest-cost command) for designating a position, which is accessible atthe shortest (or smallest) access cost from the current position, as anext processing command from the queue commands, and changes the orderof the lowest-cost command selected from the queue commands to the nextorder. As described above, the command control unit 620 calculatesaccess costs corresponding to the queue commands of the own actuator ACand other actuator AC based on the reordering information, selects alowest-cost command from the queue commands based on the result of thecalculation of the access costs, performs a reordering arithmeticprocess of changing the order of the selected lowest-cost command to thenext order, and processes the lowest-cost command after (or during) theprocessing of the current command. The command control unit 620 maycalculate a plurality of access costs of the queue commands of the ownactuator AC and other actuator AC stored in a queue for each interfaceIF (or the actuator AC) based on the reordering information other thanthe reordering table, select a low-cost command (or the lowest-costcommand) from the queue commands as a next-processed command based onthe reordering information other than the reordering table and theresult of the calculation of the access costs, change the order of theselected low-cost command (or the lowest-cost command) to the nextorder, and process the low-cost command (or the lowest-cost command)after (or during) the processing or the current command.

For example, based on the reordering information such as the current andfuture operating states of the own actuator AC and otter actuator AC andthe result of calculation of the access costs of the queue commands ofthe own actuator AC (or the other actuator AC) stored in the queue foreach interface IF (or the actuator AC), the command control unit 620selects, as the next processed-command, a lowest-cost command, which iscapable of minimizing performance degradation due to mutual interferencebetween the own actuator AC and the other actuator AC, from the queuecommands of the own actuator AC (or the other actuator AC), and changesthe order of the lowest-cost command selected from the queue commands ofthe own actuator AC (or the other actuator AC) to the next order.

For example, when the other actuator AC does not process the command,the command control unit 620 selects a lowest-cost command as anext-processed command from the queue commands of the own actuator ACbased on the reordering information such as the current and futureoperating states of the own actuator AC and other actuator AC and theresult of calculation of the access cost of each of the queue commandsof the own actuator AC stored in the queue for each interface IF (or theactuator AC), and changes the order of the lowest-cost command selectedfrom the queue commands of the own actuator AC to the next order.

For example, when the command control unit 620 determines that the otheractuator AC is performing a read/write operation and terminates theread/write operation in a short time, it selects, as a next-processedcommand, a lowest-cost command, which specifies a position accessible atthe shortest (or smallest) access cost from the timing when the otheractuator AC terminated its read/write operation, from the queue commandsof the own actuator AC, based on the reordering information such as thecurrent and future operating states of the own actuator AC and otheractuator AC and the result of calculation of the access cost of each ofthe queue commands of the own actuator AC stored in the queue for eachinterface IF (or the actuator AC), and changes the order of thelowest-cost command selected from the queue commands of the own actuatorAC to the following order.

For example, when the command control unit 620 determines that the otheractuator AC is performing its read/write operation and a long time isrequired to terminate the read/write operation, it selects, as anext-processed command, a lowest-cost command, which specifies aposition accessible at the shortest (or smallest) access cost under aseek condition that the read/write operation can be performed with aseek current such that the read/write operation is not influenced by themutual interference between the own actuator AC and the other actuatorAC, from the queue commands of the own actuator AC, based on thereordering information such as the current and future operating statesof the own actuator AC and other actuator AC and the result ofcalculation of the access cost of each of the queue commands of the ownactuator AC and other actuator AC stored in the queue for each interfaceIF (or the actuator AC), and changes the lowest-cost command selectedfrom the queue commands of the own actuator AC to the next order.

For example, when the other actuator AC is performing its read/writeoperation, the command control unit 620 selects a lowest-cost command asa next-processed command from the queue commands of the own actuator AC,based on the current and future operating states of the own actuator ACand other actuator AC and the result of calculation of the access costof each of the queue commands of the own actuator AC and other actuatorAC stored in the queue for each interface IF (or the actuator AC). Thecommand control unit 620 predicts timing influenced by mutualinterference between the own actuator AC and the other actuator AC bythe seek operation of the other actuator AC. When a read operation or awrite operation corresponding to the other actuator AC is performed atthe timing of the selected command (e.g., the lowest-cost command), thecommand control unit 620 excludes the selected command (e.g., thelowest-cost command). When the write or read operation corresponding tothe other actuator AC is performed at the timing of the selected command(e.g., the lowest-cost command), the command control unit 620 selects,as a next processed-command, a lowest-cost command from the queuecommands other than the excluded command based on the current and futureoperating states of the own actuator AC and other actuator AC and theresult of calculation of the access cost of each of the queue commandsof the own actuator AC and other actuator AC stored in the queue foreach interface IF (or the actuator AC). When the write or read operationcorresponding to the other actuator AC is not performed at the timing ofthe selected command (e.g., the lowest-cost command), the commandcontrol unit 620 changes the order of the lowest-cost command selectedfrom the queue commands to the next order. Note that the timinginfluenced by the seek operation of the other actuator AC variesaccording to whether a write operation or a read operation is performed.For example, the read operation is less influenced.

For example, the command control unit 620 may add information on themutual interference between the own actuator AC and the other actuatorAC to the reordering table to execute reordering in accordance with an,allowable level of the mutual interference between the own actuator ACand the other actuator AC. The allowable level of the mutualinterference between the own actuator AC and the other actuator ACvaries according to whether a command under execution indicates a writeoperation or a read operation, a combination of head numbers, a relativeradial position of the mutual interference between the head HD of theown actuator AC and that of the other actuator AC, etc. For this reason,a seek profile table may be provided for each condition, or variousconditions may be calculated as parameters for a base seek profiletable.

The command control unit 620 counts the number of queue commands (whichmay also be referred to as a queue command number hereinafter). Thecommand control unit 620 counts the number of queue commandscorresponding to each actuator AC in at least one queue command.

The command control unit 620 includes a command storage unit 6200, afirst reordering arithmetic operation unit 621; which performs areordering arithmetic process for a plurality of queue commandscorresponding to the actuator AC0, and a second reordering arithmeticoperation unit 6211 which performs a reordering arithmetic process for aplurality of queue commands corresponding to the actuator AC1. Note thattwo or more command control units 620 may be provided depending on thenumber of actuators AC.

The command storage unit 6200 includes a queue. The command storage unit6200 may include a plural-ty of queues corresponding to their respectiveactuators AC or may include a combination of queues (which may also bereferred to as a composite queue) corresponding to the actuators AC. Forexample, the command storage unit 6200 way include a queue correspondingto the actuator AC0 and a queue corresponding to the actuator AC1 or mayinclude a combination of queues corresponding to the actuators AC0 andAC1.

The command storage unit 6200 stores a command received from the host100 or the like in a queue. For example, the command storage unit 6200may store, in the composite queue, a plurality of commands correspondingto the actuator AC0 received from the host 100 or the like and aplurality of commands corresponding to the actuator AC1 received fromthe host 100 or the like in the order received from the host 100 or thelike from the same direction. The command storage unit 6200 may store aplurality of commands corresponding to the actuator AC0 received fromthe host 100 or the like in the composite queue in the order receivedfrom the host 100 or the like, and may store a plurality of commandscorresponding to the actuator AC1 received from the host 100 or the likein the composite queue in the order received from the host 100 or thelike from the direction opposite to the commands corresponding to theactuator AC0.

The command storage unit. 6200 can store commands corresponding to thenumber of commands (which may also be referred to as a queue depth (QD))that can be stored in a queue specified by the host 100 or the like.When the number of queue commands corresponding to a particular actuatorAC is the number of commands corresponding to the QD corresponding tothe actuator AC, the command storage unit 6200 does not receive anycommand corresponding to the actuator AC from the host 100 or the like.When the number of queue commands corresponding to a particular actuatorAC is smaller than the 0D corresponding to the actuator AC, the commandstorage unit 6200 stores commands corresponding to the actuator ACreceived from the host 100 or the like in a queue. For example, when theQD corresponding to the actuator AC1 is three and the number of queuecommands corresponding to the actuator AC1 is three, the command storageunit 6200 does not receive any command corresponding to the actuator AC1from the host 100 or the like. When the QD corresponding to the actuatorAC1 is three and the number of queue commands corresponding to theactuator AC1 is two, the command storage unit 6200 stores the commandscorresponding to the actuator ACM received from the host 100 or the likein a queue corresponding to the actuator AC1.

FIG. 3 is a schematic diagram showing an example of queues Q0 and Q1. InFIG. 3, the command storage unit 6200 includes a queue Q0 for storing acommand corresponding to the actuator AC0 and a queue Q1 for storing acommand corresponding to the actuator AC1. In the example shown in FIG.3, the QD of the queues Q0 and Q1 is three. The QD of the queues Q0 andQ1 may be two or less and four or more. In FIG. 3, the queue Q0 storescommands Cmd00 e, Cmd01 e and Cmd02 e. The commands Cd00 e, Cmd01 e andCmd02 e are transferred from the host 100 or the like in the orderpresented. The commands Cmd00 e, Cmd01 e and Cmd02 e correspond to theactuator AC0. In FIG. 3, the queue Q1 stores commands Cmd10 e and Cmd11e. The commands Cmd10 e and Cmd11 e are transferred from the host 100 orthe like in the order presented. The commands Cmd10 e and Cmd11 ecorrespond to the actuator AC1. FIG. 3 shows a direction CD0 in which acommand is stored in the queue Q0 (which may also be referred to as astorage direction) and a direction CD1 in which a command is stored inthe queue Q1.

In the example shown in FIG. 3, the command storage unit 6200 stores thecommands Cmd00 e, Cmd01 e and Cmd02 e in the queue Q0 in the orderpresented along the storage direction CD0, and stores the commands Cmd10e and Cmd11 e in the queue Q1 in the order presented along the storagedirection CD1.

Since the number of queue commands (=3) corresponding to the actuatorAC0 stored in the queue QC is the number of commands (=3) correspondingto the QD, the command storage unit 6200 does not receive the commandcorresponding to the actuator AC0 from the host 100 or the like. Sincethe number of queue commands (=2) corresponding to the actuator AC1stored in the queue Q1 is smaller than QD (=3), the command storage unit6200 can receive a command corresponding to the actuator AC1 from thehost 100 or the like and store it in the queue Q1.

The first reordering arithmetic operation unit 6210 performs areordering arithmetic process for a plurality of queue commandscorresponding to the actuator AC0. For example, during the processing ofthe current command, the first reordering arithmetic operation unit 6210performs a reordering arithmetic process for a plurality of queuecommands corresponding to the actuator ACC received from the host 100 orthe like.

In one example, based on information on the current position of the headHD0, information on a plurality of queue commands corresponding to theactuator AC0, and reordering information corresponding to the actuatorAC0, such as a reordering table corresponding to the actuator AC0, thefirst reordering arithmetic operation unit 6210 calculates an accesscost (which may also be referred to as a next-estimated costhereinafter) from the current position of the head HD0 to a plurality ofpositions respectively designated by a plurality of queue commands(which way also be referred to as the next-processed prospect commandshereinafter) which may be processed next to the current command amongthe queue commands corresponding to the actuator AC0. In order to reducethe influence of vibration and power consumption of the magnetic diskdevice 1, the first reordering arithmetic operation unit 6210 may adjustthe calculated access cost (next-estimated cost) by weighting the accesscost (next-estimated cost) (e.g., multiplying or dividing a given value)and radially offsetting the position of the disk DK0 where the head HD0starts to move and the position of the disk DK0 where the head HD0 moves(e.g., adding or subtracting a given value). Based on the result ofcalculation of the next-estimated cost, the first reordering arithmeticoperation unit 6210 selects a low-cost command (or a lowest-costcommand) from the next-processed prospect commands and changes the orderof the low-cost command (or the lowest-cost command) selected from thenext-processed prospect commands to the next order.

The first reordering arithmetic operation unit 6210 may record, forexample, reordering information corresponding to the actuator AC0 in aparticular recording area, for example, the system area DKb0 of the diskDK0, the volatile memory 70, the buffer memory 80, and the nonvolatilememory 90. Note that the first reordering arithmetic operation unit 6210may record reordering information corresponding to the actuator AC0other than the reordering table corresponding to the actuator AC0 in aparticular recording area, for example, the system area DKb0 of the diskDK0, the volatile memory 70, the buffer memory 80, and the nonvolatilememory 90. In this case, the first reordering arithmetic operation unit6210 may record a reordering table corresponding to the actuator AC0 ina particular recording area, for example, the system area DKb0 of thedisk DK0, the volatile memory 70, the buffer memory 80, and thenonvolatile memory 90, separately from the reordering informationcorresponding to the actuator AC0. The first reordering arithmeticoperation unit 6210 may record a reordering table corresponding to eachactuator AC, for example, a reordering table corresponding to theactuator AC0 and a reordering table corresponding to the actuator AC1,in a particular recording area, for example, the system area DKb0 of thedisk DK0, the volatile memory 70, the buffer memory 80, and thenonvolatile memory 90. The first reordering arithmetic operation unit6210 may also record reordering tables corresponding to a plurality ofactuators AC, for example, reordering tables corresponding to theactuators AC0 and AC1, in a particular recording area, for example, thesystem area DKb0 of the disk DK0, the volatile memory 70, the buffermemory 80, and the nonvolatile memory 90. The first reorderingarithmetic operation unit 6210 may obtain a reordering tablecorresponding to the actuator AC1 by calculation. The first reorderingarithmetic operation unit 6210 may obtain a reordering tablecorresponding to the actuator AC0 and a reordering table correspondingto the actuator ACM by calculation. The first reordering arithmeticoperation unit 6210 may obtain reordering tables corresponding to theactuators AC0 and AC1 by calculation.

The second reordering arithmetic operation unit 6211 performs areordering arithmetic process for a plurality or queue commandscorresponding to the actuator AC1. For example, during the processing ofthe current command, the second reordering arithmetic operation unit6211 performs a reordering arithmetic process for a plurality of queuecommands corresponding to the actuator AC1 received from the host 100 orthe like.

In one example, based on information on the current position of the headHD1, information on a plurality of queue commands corresponding to theactuator AC1, and reordering information corresponding to the actuatorAC1, such as a reordering table corresponding to the actuator AC1, thesecond reordering arithmetic operation unit 6211 calculates a pluralityof next-estimated costs from the current position of the head HD1 to aplurality of positions respectively designated by a plurality ofnext-processed prospect commands of the queue commands corresponding tothe actuator AC1. In order to reduce the influence of vibration andpower consumption of the magnetic disk device 1, the second reorderingarithmetic operation unit 6211 may adjust the calculated access costs(next-estimated costs) by weighting the access costs (next-estimatedcosts) (e.g., multiplying or dividing a given value) and radiallyoffsetting the position of the disk DK1 where the head HD1 starts tomove and the position of the disk DK1 where the head HD1 moves (e.g.,adding or subtracting a given value). Based on the result of calculationof the next-estimated costs, the second reordering arithmetic operationunit 6211 selects a low-cost command (or a lowest-cost command) from thenext-processed prospect commands and changes the order of the low-costcommand (or the lowest-cost command) selected from the next-processedprospect commands to the next order. The reordering table correspondingto the actuator AC1 may be the same as or different from the reorderingtable corresponding to the actuator AC0.

The second reordering arithmetic operation unit 6211 may record, forexample, reordering information corresponding to the actuator AC1 in aparticular recording area, for example, the system area DKb1 of the diskDF1, the volatile memory 70, the buffer memory 80, and the nonvolatilememory 90. Note that the second reordering arithmetic operation unit6211 may record reordering information corresponding to the actuator AC1other than the reordering table corresponding to the actuator AC1 in aparticular recording area, for example, the system area DKb1 of the diskDK1, the volatile memory 70, the buffer memory 80, and the nonvolatilememory 90. In this case, the second reordering arithmetic operation unit6211 may record a reordering table corresponding to the actuator AC1 ina particular recording area, for example, the system area DKb1 of thedisk DK1, the volatile memory 70, the buffer memory 80, and thenonvolatile memory 90, separately from the reordering informationcorresponding to the actuator AC. The second reordering arithmeticoperation unit 6211 may record a reordering table corresponding to eachactuator AC, for example, a reordering table corresponding to theactuator AC0 and a reordering table corresponding to the actuator AC1,in a particular recording area, for example, the system area DKb1 of thedisk DK1, the volatile memory 70, the buffer memory 80, and thenonvolatile memory 90. The second reordering arithmetic operation unit6211 may also record reordering tables corresponding to a plurality ofactuators AC, for example, reordering tables corresponding to theactuators AC0 and AC1, in a particular recording area, for example, thesystem area DKb1 of the disk DK1, the volatile memory 70, the buffermemory 80, and the nonvolatile memory 90. The second reorderingarithmetic operation unit 6211 may obtain a reordering tablecorresponding to the actuator AC1 by calculation. The second reorderingarithmetic operation unit 6211 may obtain a reordering tablecorresponding to the actuator AC0 and a reordering table correspondingto the actuator AC1 by calculation. The second reordering arithmeticoperation unit 6211 may obtain reordering tables corresponding to theactuators AC0 and AC1 by calculation.

Based on the result of calculation of the access cost of each of thequeue commands corresponding to the actuator AC1, the second reorderingarithmetic operation unit 6211 selects a low-cost command (or alowest-cost command) from the queue commands corresponding to theactuator AC1, and changes the order of the low-cost command (or thelowest-cost command; selected from the queue commands to the next order.

In one example, based on the result of calculation of somenext-estimated costs of some next-processed prospect commands of thequeue commands corresponding to the actuator AC1, the second reorderingarithmetic operation unit 6211 selects a low-cost command (or alowest-cost command) from the queue commands corresponding to theactuator AC1, and changes the order of the low-cost command (or thelowest-cost command; selected from the next-processed prospect commandscorresponding to the actuator AC1 to the next order.

FIG. 4 is a time sequence showing an example of the reordering processaccording to the present embodiment. FIG. 4 shows an IF0 access requestthat is input and output to and from the actuator AC) via the interfaceIF0 and an IF1 access request that is input and output to and from theactuator AC1 via the interface IF1. FIG. 4 shows queues Q0 and Q1. Asshown in FIG. 4, the queue Q0 may store commands (queue commands) Cmd00,Cmd01, Cmd02, Cmd03 and Cmd04, and the queue Q1 may store commands(queue commands) Cmd10, Cmd21, Cmd12, Cmd13 and Cmd14. FIG. 4 shows acommand process (or a read/write operation) of the actuator AC0 and acommand process (or a read/write operation) of the actuator AC1. Assumein FIG. 4 that time t elapses toward the head of the arrow. That is, inFIG. 4, the direction toward the head of the arrow corresponds to thefuture of time t and its opposite direction corresponds to the past oftime t.

In the example shown in FIG. 4, during the read/write operation in theactuator AC0, the system controller 130 acquires information on the seekoperation of the head HD0 in the read/write operation of the actuatorAC0 and information on the start timing and end timing of the read/writeoperation of the head HD0. During the read/write process in the actuatorAC0, the system controller 130 selects lowest-cost command Cmd12 fromthe queue commands Cmd10, Cmd11, Cmd12 and Cmd13 stored in the queue Q1of the actuator AC1, and changes the order of the selected lowest-costcommand Cmd12 to the next order. The system controller 130 causes theactuator AC1 to start the read/write operation of the command Cmd12.

In the example shown in FIG. 4, during the read/write operationcorresponding to the command Cmd12 in the actuator AC1, the systemcontroller 130 acquires information on the seek operation of the headHD1 in the read/write operation corresponding to the command Cmd12 inthe actuator AC1 and information on the start timing and end timing ofthe read/write operation of the head HD1 corresponding to the commandCmd12. The system controller 130 selects a lowest-cost command Cmd03,which specifies a position accessible at the lowest access cost from thetiming when the read/write operation is terminated in the actuator AC0,from the commands Cmd00, Cmd01, Cmd02 and Cmd03 stored in the queue Q0of the actuator AC0, and changes the order of the selected lowest-costcommand Cmd03 to the next order. After the read/write operation isterminated in the actuator AC0, the system controller 130 causes theactuator AC0 to start a read/write operation corresponding to thecommand Cmd03.

In the example shown in FIG. 4, during the read/write operationcorresponding to the command Cmd03 in the actuator AC0, the systemcontroller 130 acquires information on the seek operation of the headHD0 in the read/write operation corresponding to the command Cmd03 inthe actuator AC0 and information on the start timing and end timing ofthe read/write operation of the head HD0 corresponding to the commandCmd03. When the read/write operation corresponding to the command Cmd12is terminated during the read/write operation corresponding to thecommand Cmd03 in the actuator AC0, the system controller 130 receivesthe termination of the read/write operation corresponding to the commandCmd12 via the interface IF1. The system controller 130 acquiresinformation that there is a free space in the queue Q1 corresponding tothe actuator AC1. The system controller 130 selects a lowest-costcommand Cmd11, which specifies a position accessible at the lowestaccess cost from the timing when the read/write operation correspondingto the command Cmd12 is terminated in the actuator AC1, from thecommands Cmd10, Cmd11 and Cmd13 stored in the queue Q1 of the actuatorAC1, and changes the order of the selected lowest-cost command Cmd11 tothe next order. After the read/write operation corresponding to thecommand Cmd12 is terminated in the actuator AC1, the system controller130 causes the actuator AC1 to start a read/write operationcorresponding to the command Cmd11.

In the example shown in FIG. 4, during the read/write operationcorresponding to the command Cmd11 in the actuator AC1, the systemcontroller 130 acquires information on the seek operation of the headHD1 in the read/write operation corresponding to the command Cmd11 inthe actuator AC1 and information on the start timing and end timing ofthe read/write operation of the head HD1 corresponding to the commandCmd11. When the read/write operation corresponding to the command Cmd03is terminated during the read/write operation corresponding to thecommand Cmd11 in the actuator AC1, the system controller 130 receivesthe termination of the read/write operation corresponding to the commandCmd03 via the interface IF0. The system controller 130 acquiresinformation that there is a free space in the queue Q0 corresponding tothe actuator AC0.

The system controller 130 selects a lowest-cost command Cmd00, whichspecifies a position accessible at the lowest access cost from thetiming when the read/write operation corresponding to the command Cmd03is terminated in the actuator AC0, from the commands Cmd00, Cmd01 andCmd02 stored in the queue Q0 of the actuator AC0, and changes the orderof the selected lowest-cost command Cmd00 to the next order. After theread/write operation corresponding to the command Cmd03 is terminated inthe actuator AC0, the system controller 130 causes the actuator AC0 tostart a read/write operation corresponding to the command Cmd00.

The system controller 130 receives the command Cmd14 via the interfaceIF1 during the read/write operation corresponding to the command Cmd11in the actuator AC1.

The system controller 130 receives the command Cmd04 via the interfaceIF0 during the read/write operation corresponding to the command Cmd11in the actuator AC1.

In the example shown in FIG. 4, during the read/write operationcorresponding to the command Cmd00 in the actuator ACC, the systemcontroller 130 acquires information on the seek operation of the headHD0 in the read/write operation corresponding to the command Cmd00 inthe actuator AC0 and information on the start timing and end timing ofthe read/write operation of the head HD0 corresponding to the commandCmd00. When the read/write operation corresponding to the command Cmd11is terminated during the read/write operation corresponding to thecommand Cmd00 in the actuator AC0, the system controller 130 receivesthe termination of the read/write operation corresponding to the commandCmd11 via the interface IF1. The system controller 130 acquiresinformation that there is a free space in the queue Q1 corresponding tothe actuator AC1.

The system controller 130 selects a lowest-cost command Cmd13, whichspecifies a position accessible at the lowest access cost from thetiming when the read/write operation corresponding to the command Cmd11is terminated in the actuator AC1, from the commands Cmd10, Cmd13 andCmd14 stored in the queue Q1 of the actuator AC1, and changes the orderof the selected lowest-cost command Cmd13 to the next order. After theread/write operation corresponding to the command Cmd11 is terminated inthe actuator AC1, the system controller 130 causes the actuator AC1 tostart a read/write operation corresponding to the command Cmd13.

FIG. 5 is a schematic diagram showing an example of the read/writeoperation according to the present embodiment. FIG. 5 shows variationsSCL in seek current with time t (which may also be referred to as seekcurrent variations hereinafter). The horizontal axis of the seek currentvariations SCL indicates time t, and the vertical axis thereof indicatesa seek current. In the horizontal axis, time t elapses toward the headof the arrow. In the vertical axis, the seek current increases inpositive value toward the positive direction of the double-headed arrowrelative to the origin (=0), and decreases in negative value toward thenegative direction of the double-headed arrow relative to the origin(=0). FIG. 5 also shows variations HPL in head position with time t(which may also be referred to as head position variations hereinafter).The horizontal axis of the head position variations HPL indicates timet, and the vertical axis thereof indicates a head position. In thehorizontal axis, time t elapses toward the head of the arrow. In thevertical axis thereof, the head position moves outward toward theoutward direction of the double-headed arrow, and moves inward towardthe inward direction of the double-headed arrow. Note that in thevertical axis of the head position variations HPL, the “outward” and the“inward” may be reversed. In addition, FIG. 5 shows a flag SMF duringseek operation for time t (which may also be referred to as a seekoperating flag hereinafter), a flag WRPF during read/write operation fortime t (which may also be referred to as a read/write operating flaghereinafter), and a flag CPF during command processing for time t (whichmay also be referred to as a command processing flag hereinafter). Theseek operating flag SMF, read/write operating flag WRPF and commandprocessing flag CPF are ON when they rise and OFF when they fall.

In the example shown in FIG. 5, the system controller 130 turns on thecommand processing flag CPF to start command processing (or read/writeoperation). Upon turning on the command processing flag CPF, the systemcontroller 130 turns on the seek operating flag SMF to start the seekoperation of the head HD. Upon turning on the seek operating flag SMF,the system controller 130 increases the seek current variations SCLtoward the positive value. The system controller 130 moves the head HDfrom inside to outside (or changes the head position variations HPL frominside to outside).

The system controller 130 turns off the seek operating flag SMF toterminate the seek operation of the head HD. Upon turning off the seekoperating flag SMF, the system controller 130 decreases the seek currentvariations SCL toward the negative value.

After a rotational delay from when the system controller 130 turns offthe seeking operation flag, it turns on the R/W operating flag WRPF tostart a R/W operation.

The system controller 130 turns off the R/W operating flag WRPF toterminate the P/W operation. Upon turning off the R/W processing flagWRPF, the system controller 130 turns off the command processing flagCPF to terminate the command processing (or read/write operation).

FIG. 6 is a schematic diagram showing an example of variations SCL00 ofa seek current corresponding to the head HD00 of the actuator AC0 andvariations PESL10 of a position error signal of the head HD10 of theactuator AC1 according to the present embodiment. FIG. 6 showsvariations SCL00 in a seek current with time t corresponding to the headHD00 (or the head HD01) of the actuator AC0 (which may also be referredto as seek current variations hereinafter). The horizontal axis of theseek current variations SCL00 indicates time t, and the vertical axisthereof indicates a seek current. In the horizontal axis, time t elapsestoward the head of the arrow. In the vertical axis, the seek currentincreases in positive value toward the positive direction of thedouble-headed arrow relative to the origin (=0), and decreases innegative value toward the negative direction of the double-headed arrowrelative to the origin (=0). The vertical axis of the seek currentvariations SCL00 indicates a seek current CRT0 and a seek current −CRT0.In FIG. 6, the seek current variations SCL00 corresponding to the headHD00 (or the head HD01) of the actuator AC0 is the maximum in the seekcurrent CRT0 and the minimum in the seek current −CRT0. The absolutevalue of the seek current CRT0 and the absolute value of the seekcurrent −CRT0 may be the same or different from each other. FIG. 6 alsoshows variations PESL10 in position error signal with time tcorresponding to the head HD10 (or the HD11) of the actuator AC1 (whichmay also be referred to as position error signal variationshereinafter). The horizontal axis of the position error signalvariations PESL10 indicates time t, and the vertical axis thereofindicates a position error signal. In the horizontal axis, time telapses toward the head of the arrow. In the vertical axis, the positionerror signal increases in positive value toward the positive directionof the double-headed arrow relative to the origin (=0), and decreases innegative value toward the negative direction of the double-headed arrowrelative to the origin (=0). The vertical axis of the position errorsignal variations PESL10 indicates a position error signal PES0 and aposition error signal −PES0. In FIG. 6, the position error signalvariations PESL10 of the head HD10 (or the head HD11; of the actuatorAC1 are made in the range of the position error signals PES0 to −PES0.The absolute value of the position error signal PES0 and the absolutevalue of the position error signal −PES0 may be the same or differentfrom each other.

In the example shown in FIG. 6, the system controller 130 applies a seekcurrent to the actuator AC0 to seek the head HD00 (or the HD01) andcause the head HD10 (or the HD11) of the actuator ACM to access aparticular area of the disk DK1. The position error signal variationsPESL10 in a particular area accessed by the head HD10 (or the head HD11)of the actuator AC1 are made according to the seek current variationsSCL00 corresponding to the head HD00 (or the head HD01) of the actuatorAC0. That is, when a seek current is applied to the actuator AC0 to seekthe head HD00 (or the HD01), a position error signal in a particulararea accessed by the head HD10 (or the head HD11) of the actuator AC1 isinfluenced. Even though a seek current is applied to the actuator AC1 toseek the head HD10 (or the HD11) and to access a particular area of thedisk DK0 by the head HD01 (or the head HD00) of the actuator AC0, aninfluence similar to that when a seek current is applied to the actuatorAC0 to seek the head HD00 (or the HD01) and to access a particular areaof the disk DK1 by the head HD10 (or the head HD11) of the actuator AC1,may be caused.

FIG. 7 is a schematic diagram showing an example of variations SCL01 ofa seek current corresponding to the head HD00 of the actuator AC0 andvariations PESL11 of a position error signal of the head HD11 of theactuator AC1 according to the present embodiment.

FIG. 7 shows variations SCL01 in the seek current corresponding to thehead HD00 (or the head HD01) of the actuator AC0. The horizontal axis ofthe seek current variations SCL01 indicates time t, and the verticalaxis thereof indicates a seek current. In the horizontal axis, time telapses toward the head of the arrow. In the vertical axis, the seekcurrent increases in positive value toward the positive direction of thedouble-headed arrow relative to the origin (=0), and decreases innegative value toward the negative direction of the double-headed arrowrelative to the origin (=0). The vertical axis of the seek currentvariations SCL01 indicates a seek current CRT1 and a seek current −CRT1.In FIG. 7, the seek current variations SCL01 corresponding to the headHD00 (or the head HD0) of the actuator AC0 is the maximum in the seekcurrent CRT1 and the minimum in the seek current −CRT1. The absolutevalue of the seek current CRT1 and the absolute value of the seekcurrent −CRT1 may be the same or different from each other. FIG. 7 alsoshows position error signal variations PESL11 corresponding to the headHD11 (or the HD10) of the actuator AC1. The horizontal axis of theposition error signal variations PESL11 indicates time t, and thevertical axis thereof indicates a position error signal. In thehorizontal axis, time t elapses toward the head of the arrow. In thevertical axis, the position error signal increases in positive valuetoward the positive direction of the double-headed arrow relative to theorigin (=0), and decreases in negative value toward the negativedirection of the double-headed arrow relative to the origin (=0). Thevertical axis of the position error signal variations PESL11 indicates aposition error signal PES1 and a position error signal −PES1. In PTG. 7,the position error signal variations PESL11 of the head HD11 (or thehead HD10) of the actuator AC1 are made in the range of the positionerror signals PES1 to −PES1. The absolute value of the position errorsignal PES1 and the absolute value of the position error signal −PES1may be the same or different from each other.

In the example shown in FIG. 7, the system controller 130 applies a seekcurrent to the actuator AC0 to seek the head HD00 (or the HD01) andcause the head HD11 (or the HD10) of the actuator ACM to access aparticular area of the disk DK1. The position error signal variationsPESL11 in a particular area accessed by the head HD11 (or the head HD10)of the actuator AC1 are made according to the seek current variationsSCL01 corresponding to the head HD01 (or the head HD00) of the actuatorAC0. That is, when a seek current is applied to the actuator AC0 to seekthe head HD00 (or the HD01), a position error signal in a particulararea accessed by the head HD11 (or the head HD10) of the actuator AC1 isinfluenced. FIGS. 6 and 7 shows that when the same seek current isapplied to actuator AC0, the influence to the head HD10 and the headHD11 are similar but the absolute values of PES0 and PES1 are not thesame. Even though a seek current is applied to the actuator AC1 to seekthe head HD11 (or the HD10) and to access a particular area of the diskDK0 by the head HD01 (or the head HD00) of the actuator AC0, aninfluence similar to that when a seek current is applied to the actuatorAC0 to seek the head HD01 (or the HD00) and to access a particular areaof the disk DK1 by the head HD11 (or the head HD10) of the actuator AC1,may be caused.

FIG. 8 is a schematic diagram showing an example of variations SCL02 ofa seek current corresponding to the head HD00 of the actuator AC0 andvariations PESL12 of a position error signal of the head HD11 of theactuator AC1 according to the present embodiment.

FIG. 8 shows variations SCL01 in the seek current corresponding to thehead HD00 (or the head HD01) of the actuator AC0. The horizontal axis ofthe seek current variations SCL01 indicates time t, and the verticalaxis thereof indicates a seek current. In the horizontal axis, time telapses toward the head of the arrow. In the vertical axis, the seekcurrent increases in positive value toward the positive direction of thedouble-headed arrow relative to the origin (=0), and decreases innegative value toward the negative direction of the double-headed arrowrelative to the origin (=0). The vertical axis of the seek currentvariations SCL01 indicates a seek current CRT2 and a seek current −CRT2.In FIG. 8, the seek current variations SCL02 corresponding to the headHD00 (or the head HD0) of the actuator AC0 is the maximum in the seekcurrent CRT2 and the minimum in the seek current −CRT2. The absolutevalue of the seek current CRT2 and the absolute value of the seekcurrent −CRT2 may be the same or different from each other. The absolutevalue of the seek current CRT2 is smaller than the absolute value of theseek current CRT1. The absolute value of the seek current −CPT2 issmaller than the absolute value of the seek current −CRT1.

FIG. 8 also shows position error signal variations PESL12 correspondingto the head HD11 (or the HD10) of the actuator AC1. The horizontal axisof the position error signal variations PESL12 indicates time t, and thevertical axis thereof indicates a position error signal. In thehorizontal axis, time t elapses toward the head of the arrow. In thevertical axis, the position error signal increases in positive valuetoward the positive direction of the double-headed arrow relative to theorigin (=0), and decreases in negative value toward the negativedirection of the double-headed arrow relative to the origin (=0). Thevertical axis of the position error signal variations PESL12 indicates aposition error signal PES2 and a position error signal −PES2. In FIG. 8,the position error signal variations PESL12 of the head HD11 (or thehead HD10) of the actuator AC1 are made in the range of the positionerror signals PES2 to −PES2. The absolute value of the position errorsignal PES2 and the absolute value of the position error signal −PES2may be the same or different from each other. The absolute value of theposition error signal PES2 is smaller than the absolute value of theposition error signal PES1. The absolute value of the position errorsignal −PES2 is smaller than the absolute value of the position errorsignal −PES1.

In the example shown in FIG. 8, the system controller 130 applies a seekcurrent to the actuator AC0 to seek the head HD00 (or the HD01) andcause the head HD11 (or the HD10) of the actuator AC1 to access aparticular area of the disk DK1. The position error signal variationsPESL12 in a particular area accessed by the head HD11 (or the head HD10)of the actuator AC1 are made according to the seek current variationsSCL02 corresponding to the head HD00 (or the head HD01) of the actuatorAC0. That is, when a seek current is applied to the actuator AC0 to seekthe head HD00 for the HD01), a position error signal in a particulararea accessed by the head HD11 (or the head HD10) of the actuator AC1 isinfluenced. As is seen from FIGS. 6 and 7, if a seek current to beapplied to the actuator AC0 is decreased, an influence on the positionerror signal in a particular area accessed by the head HD11 (or the headHD10) of the actuator AC1 can be lessened. Even though a seek current isapplied to the actuator AC1 to seek the head HD11 (or the HD10) and toaccess a particular area of the disk DK0 by the head HD00 (or the headHD01) of the actuator AC0, an influence similar to that when a seekcurrent is applied to the actuator AC0 to seek the head HD00 for theHD01) and to access a particular area of the disk DK1 by the head HD11(or the head HD10) of the actuator AC1, may be caused.

FIG. 9 is a schematic diagram showing an example of a reordering tableaccording to the present embodiment. FIG. 9 shows variations STLG inseek time with a plurality of seek distances capable of seeking with aseek current that has no influence upon a plurality of heads HDcorresponding to their respective head numbers (which may also bereferred to as a seek time variation group hereinafter), and variationsFSTL in seek time with a seek distance at the time of the earliest seek(referred to earliest seek time variations hereinafter). The seek timevariation group STLG includes variations STL0 in seek time with a seekdistance capable of seeking with a seek current that has no influenceupon the head ID of head number 0, for example, the head HD00 or HD10(which may also be referred to as a seek time variation hereinafter) andvariations STLN in seek time capable of seeking with a seek current thathas no influence upon the head HD of head number N, for example, thehead HD01 or HD11. The horizontal axis of the seek time variation (orthe reordering table) indicates a seek distance, and the vertical axisthereof indicates seek time. In the horizontal axis, the seek distanceincreases toward the “large” direction of the double-headed arrow anddecreases the “small” direction thereof. In the vertical axis, the seektime increases toward the “long” direction of the double-headed arrowand decreases the “short” direction thereof.

In the example shown in FIG. 9, the system controller 130 may addinformation on mutual interference of the own and other actuators AC tothe reordering table shown in FIG. 9 to perform a reordering processaccording to the level of allowable mutual interference of the own andother actuators AC. Based on the current and future operating states ofthe own and other actuators AC, the current position of the head HDcorresponding to the own actuator AC, a plurality of queue commandsstored in the queue for each interface IF (or actuator AC) in the orderreceived from the host 100 or the like, and the reordering table shownin FIG. 9, the system controller 130 may calculate a plurality of timesfor gaining access to each of the positions of a plurality of sectors(data sectors) of the disk DK designated by the queue commands from thecurrent position.

FIG. 10 is a flowchart showing an example of the reordering processaccording to the present embodiment.

The system controller 130 determines whether the other actuator AC isexecuting a command (B1001). When the system controller 130 determinesthat the other actuator AC is not executing a command (NO in B1001), itexecutes a lowest-cost command from a plurality of queue commands of theown actuator AC (B1002) and terminates the process. For example, thesystem controller 130 executes a command that can be executed earliestby the own actuator AC and terminates the process.

It the system controller 130 determines that the other actuator AC isexecuting a command (YES in B1001), it determines whether the otheractuator AC is performing a write or read operation (B1003). When thesystem controller 130 determines that the other actuator AC is notperforming a write or read operation (NO in B1003), it calculates starttiming (scheduled time) when the other actuator starts to perform awrite or read operation (B1004), and selects, as a next-processedcommand, a lowest-cost command that can be executed earliest, from thequeue commands of the own actuator AC based on the start timing when theother actuator starts to perform the write or read operation (B1005).When a command selected from the queue commands of the own actuator ACis influenced by the seek operation of the other actuator AC, the systemcontroller 130 excludes the selected command and proceeds to step B1005.When the command selected from the queue commands of the own actuator ACis not affected by the seek operation of the other actuator AC, thesystem controller 130 proceeds to step B1007 (B1006). When a commandselected from the queue commands of the own actuator AC influences thewrite or read operation of the other actuator AC, the system controller130 excludes the selected command and proceeds to step B1005. When thecommand selected from the queue commands of the own actuator AC has noinfluence upon the write or read operation of the other actuator AC(B1007), the system controller 130 executes the selected command andterminates the process.

If the system controller 130 determines that the other actuator AC isperforming a write or read operation (YES in B1003), it determineswhether the write or read operation is terminated in a short time or not(B1008). When the system controller 130 determines that the write orread operation or the other actuator AC is not terminated in a shorttime, that is, it takes a long time to terminate the operation (No inB1008), it selects, as a next-processed command, a lowest-cost commandthat can be executed earliest under a seek condition with a seek currentthat does has no influence upon the write or read operation of the otheractuator, from the queue commands of the own actuator AC (B1009),executes the selected command, and terminates the process. When thesystem controller 130 determines that the write or read operation of theother actuator AC is terminated in a short time (Yes in B1008), itselects, as a next-processed command, a lowest-cost command, which canbe executed earliest from the end timing (scheduled end time) of thewrite or read operation of the other actuator AC, from the queuecommands of the own actuator AC (B1010), executes the selected command,and terminates the process.

According to the present embodiment, the magnetic disk device 1 includesa plurality of actuators AC. The magnetic disk device 1 calculates eachof a plurality of access costs of a plurality of queue commands of anown actuator AC stored in a queue for each interface IF (or actuator AC)based on reordering information. Based on the reordering information andthe result of calculation of the access costs, the magnetic disk device1 selects, as a next-processed command, a lowest-cost command capable ofminimizing performance degradation due to mutual interference of the ownactuator AC and other actuator, from the queue commands of the ownactuator AC, and changes the order of the lowest-cost command selectedin the queue commands of the own actuator AC to the next order. Themagnetic disk device 1 can thus improve in its access performance.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk device comprising: a first disk;a second disk; a first head which writes data to the first disk andreads data from the first disk; a second head which writes data to thesecond disk and reads data from the second disk; a first actuatorincluding the first head; a second actuator including the second head;and a controller which performs a first reordering process for a commandstored in a first queue corresponding to the first actuator and performsa second reordering process for a command stored in a second queuecorresponding to the second actuator, wherein the controller selects afirst command to be executed next by the first actuator based on currentand future operating states of the second actuator, and executes thefirst command.
 2. The magnetic disk device of claim 1, wherein thecontroller selects a first command that can be executed earliest basedon an operating state of one of write and read operations of the secondactuator.
 3. The magnetic disk device of claim 2, wherein when thecontroller determines that one of the write and read operations of thesecond actuator is terminated in a short time, the controller selects afirst command that can be executed earliest from timing when one of thewrite and read operations of the second actuator is terminated.
 4. Themagnetic disk device of claim 2, wherein when the controller determinesthat a long time is required to terminate one of the write and readoperations of the second actuator, the controller selects a firstcommand that can be executed earliest under a seek condition with a seekcurrent that has no influence upon one of the write and read operationsof the second actuator.
 5. The magnetic disk device of claim 2, whereinwhen the controller determines that one of the write and read operationsof the second actuator is not performed, the controller selects a firstcommand that can be executed earliest from timing when one of the writeand read operations of the first actuator is started.
 6. The magneticdisk drive of claim 5, wherein the controller excludes the first commandfrom selection if the first command is influenced by a seek operation ofanother actuator.
 7. The magnetic disk drive of claim 6, wherein thecontroller excludes the first command from selection if the firstcommand influences one of the write and read operations of anotheractuator.
 8. The magnetic disk device of claim 1, wherein the controllerselects a first command corresponding to an allowable level of mutualinterference of the first actuator and the second actuator, based on atable showing a relationship between seek time and a seek distance of ahead including information of the mutual interference.
 9. The magneticdisk device of claim 1, wherein the controller compares the firstcommand, which causes the first head to gain access to a first targetposition of the first disk in a first time, with a second command whichcauses the second head to gain access to a second target position of thesecond disk in a second time, selects the first command to cause thefirst head to gain access to the first position in the first time thatis shorter than the second time, and executes the first command.
 10. Themagnetic disk device of claim 1, wherein the operating states include acommand executing state, a read/write operation performing state, seekstates of the first head and the second head, positions of the firsthead and the second head, velocities of the first head and the secondhead, accelerations of the first head and the second head, timing when awrite/read operation is started by the first head and the second head,and timing when the write/read operation is terminated by the first headand the second head.
 11. A reordering method applied to a magnetic diskdevice which includes a first disk, a second disk, a first head whichwrites data to the first disk and reads data from the first disk, asecond head which writes data to the second disk and reads data from thesecond disk, a first actuator including the first head, a secondactuator including the second head, and a controller which performs afirst reordering process for a command stored in a first queuecorresponding to the first actuator and performs a second reorderingprocess for a command stored in a second queue corresponding to thesecond actuator, the method comprising: selecting a first command to beexecuted next by the first actuator based on current and futureoperating states of the second actuator; and executing the firstcommand.
 12. The reordering method of claim 11, further comprising:selecting a first command that can be executed earliest based on anoperating state of one of write and read operations of the secondactuator.
 13. The reordering method of claim 12, further comprising:when the controller determines that one of the write and read operationsof the second actuator is terminated in a short time, selecting a firstcommand that can be executed earliest from timing when one of the writeand read operations of the second actuator is terminated.
 14. Thereordering method of claim 12, further comprising: when the controllerdetermines that a long time is required to terminate one of the writeand read operations of the second actuator, selecting a first commandthat can be executed earliest under a seek condition with a seek currentthat has no influence upon one of the write and read operations of thesecond actuator.
 15. The reordering method of claim 12, furthercomprising: when the controller determines that one of the write andread operations of the second actuator is not performed, selecting afirst command that can be executed earliest from timing when one of thewrite and read operations of the first actuator is started.
 16. Thereordering method of claim 15, further comprising: excluding the firstcommand from selection if the first command is influenced by a seekoperation of another actuator.
 17. The reordering method of claim 16,further comprising: excluding the first command from selection if thefirst command influences one of the write and read operations of anotheractuator.
 18. The reordering method of claim 11, further comprising:selecting a first command corresponding to an allowable level of mutualinterference of the first actuator and the second actuator, based on atable showing a relationship between seek time and a seek distance of ahead including information of the mutual interference.
 19. Thereordering method of claim 11, further comprising: comparing the firstcommand, which causes the first head to gain access to a first targetposition of the first disk in a first time, with a second command whichcauses the second head to gain access to a second target position of thesecond disk in a second time, selecting the first command to cause thefirst head to gain access to the first position in the first time thatis shorter than the second time; and executing the first command. 20.The reordering method of claim 11, wherein the operating states includea command executing state, a read/write operation performing state, seekstates of the first head and the second head, positions of the firsthead and the second head, velocities of the first head and the secondhead, accelerations of the first head and the second head, timing when awrite/read operation is started by the first head and the second head,and timing when the write/read operation is terminated by the first headand the second head.